Various methods have in the past been used and proposed for preventing oxidization of beverage in a container. As to prevention of oxidization of beverage of a roast material, Japanese Patent Application Laid-open Publication Sho 51-57863 proposes, for example, conducting all processes of extraction of beverage from coffee powder, filtering and filling of the beverage in a container and sealing of the container under pressure of inert gas. Japanese Patent Application Laid-open Publication Hei 9-262055 discloses a method for manufacturing coffee contained in a container according to which an empty container is kept in an oxygen-free state in its inside and coffee produced in the presence of inert gas or in an oxygen-free state is filled in this container, whereby all processes from raw material to filling and sealing are conducted in an oxygen-free state.
These prior art method for preventing oxidization of beverage of a roast material in a container in which all processes from extraction of beverage to filling of the beverage in a container and sealing of the container in an oxygen-free state are effective for preventing deterioration of quality of the beverage. In all of these methods, however, beverage must be subjected to sterilization by heating after filling of the beverage in a container and sealing of the container by retort treatment under a temperature from 120° C. to 125° C. for 30 minutes to 40 minutes with resulting disadvantage that this heating deteriorates quality of the beverage and, in the case of coffee, for example, fragrance and taste of just roasted coffee are lost.